Cogeneration systems are known in the art. In one form of cogeneration, the exhaust of a gas turbine generator is coupled through a transition piece to a heat recovery steam generator. During normal use, induction fans push heated exhaust air (including oxygen) from the gas turbine generator through the heat recovery steam generator. The heat recovery steam generator uses the warmed oxygen in this hot air for combustion purposes.
From time to time, either for scheduled maintenance purposes or through unexpected incident, the gas turbine generator will shut down. When this occurs, combustion air no longer flows from the exhaust to serve the needs of the heat recovery steam generator. Denial of combustion air, even for a relatively brief period of time, can cause a corresponding shut down of the heat recovery steam generator system. Unfortunately, once shut down, it can be a very time (and manpower) intensive activity to bring the heat recovery steam generator system back on-line (twelve to twenty-four hours of cycletime is not uncommon). Such cascading events and consequences render even a momentary shutdown of the gas turbine generator a serious problem.
One prior art solution has been to couple an auxiliary source of combustion-supporting air to the input of the heat recovery steam generator. During ordinary use, louvers (typically of the guillotine variety) are maintained in a closed position to prevent air from moving through the auxiliary opening and into the heat recovery steam generator. When a shutdown of the gas turbine generator is sensed, the louver is opened and the induction fans at the front end of the heat recovery steam generator push air from the auxiliary source into the heat recovery steam generator.
Unfortunately, such a solution has not been suitably reliable. Though shutdown of the gas turbine generator can and will occur from time to time, considerable time can elapse between such events. During that time, corrosion and/or mechanical incidents can occur that stymie free movement of the louver. This, in turn, can prevent the louver from properly opening when needed. When the louver cannot open properly, the heat recovery steam generator is again denied combustion air and system shutdown can again occur.
At least one other notable design concern exists. The induction fan(s) described above tends to create a relatively high pressure area in the transition piece between the exhaust of the gas turbine generator and the combustion air input of the heat recovery steam generator (10 to 14 inches of water are ordinary pressures in this regard). This pressure in the transition piece serves well to push combustion air into the heat recovery steam generator as desired, but also serves to create a backpressure on the exhaust of the gas turbine generator. The gas turbine generator is powerful enough to overcome such pressure, but efficiency of the gas turbine generator is still nevertheless somewhat impaired by this approach. Typical prior art solutions to the gas turbine generator shutdown problem noted above do little or nothing to mitigate this additional concern.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are typically not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.